This invention relates to a circuit arrangement for igniting and operating a discharge lamp, comprising
input terminals for connection to the poles of a supply voltage source, PA1 means I coupled to the input terminals for generating a current through the discharge lamp from a supply voltage delivered by the supply voltage source, which means are provided with
a control circuit for controlling the operational state of the circuit arrangement, PA2 inductive means comprising a primary winding which carries a high-frequency current during ignition and during lamp operation, and a secondary winding which is magnetically coupled to the primary winding and is electrically coupled to an impedance M for limiting the current carried by the secondary winding, and to an input of the control circuit via rectifying means.
Such a circuit arrangement is known. The means I may comprise, for example, a preconditioner such as an up-converter for generating a DC voltage from the supply voltage. Such a preconditioner is provided with a high-frequency operated switching element and with an inductive element across which a high-frequency AC voltage is present during operation of the means I. It is also possible for the means I to comprise a DC-AC converter for generating a high-frequency lamp current from a DC voltage. This DC-AC converter often uses one or several switching elements which are operated at a high frequency and an inductive element across which a high-frequency voltage is present during operation. The control circuit of the known circuit arrangement comprises means for generating control signals for rendering the switching elements of the preconditioner and/or the DC-AC converter conducting and non-conducting and controlling the operational state of the circuit arrangement in this manner. The control circuit is supplied with a DC voltage of comparatively low amplitude when the circuit arrangement is in operation. This DC voltage may be generated with the aid of the inductive element present in the preconditioner or of the inductive element present in the DC-AC converter. This inductive element then forms the inductive means mentioned in the opening paragraph and comprises a secondary winding. A high-frequency voltage is present across the primary winding during operation of the circuit arrangement. The magnetic coupling causes a high-frequency voltage to be present also across the secondary winding. The DC voltage is generated by means of the high-frequency voltage present across the secondary winding and the rectifying means and is applied to the input of the control circuit. If the inductive means form a part of the DC-AC converter, however, the amplitude of the voltage across the primary winding will often be considerably lower during preheating of the electrodes of the lamp than during stationary lamp operation.
As a result of this, the amplitude of the voltage across the secondary winding during preheating of the discharge lamp is also much lower than during stationary lamp operation. If a sufficient amount of power is to be supplied to the input of the control circuit also during preheating, it is necessary to choose the impedance value of the means M to be comparatively low. This has the result, however, that the current through the secondary winding is comparatively strong during stationary lamp operation as a result of the comparatively high voltage across the secondary winding, which means that the voltage at the input of the control circuit reaches too high a value. This latter effect may be counteracted through the use of a voltage limiter such as a zener diode. The use of such a voltage limiter does have the result that the voltage at the input of the control circuit is no longer too high, but the voltage limiter passes current continuously and accordingly dissipates power continuously, which means that the circuit arrangement functions comparatively inefficiently.